This invention relates generally to the field of disc drive storage devices, and more particularly, but not by way of limitation, to improving data writing operations by incorporating a write current shaping circuit in a head assembly of a disc drive.
Hard disc drives are used in modern computer systems to enable users to store and retrieve vast amounts of data in a fast and efficient manner. A typical disc drive is generally composed of a head/disc assembly (HDA) which houses requisite mechanical portions of the drive and a printed wiring assembly (PWA) which supports requisite electronic portions of the drive.
The HDA includes a base deck to which various components are mounted and a top cover which cooperates with the base deck to form a sealed housing to reduce particulate contamination. Within the housing, a disc stack is formed from one or more magnetic recording discs which are axially aligned for rotation by a spindle motor at a constant, high speed, such as 10,000 revolutions per minute during normal disc drive operation.
A rotary actuator assembly is mounted adjacent the disc stack and includes a plurality of rigid arms which extend into the stack between adjacent discs, as well as above and below the top and bottom discs. The rigid arms support flexible suspension assemblies which in turn, support a corresponding number of read/write heads adjacent the surfaces of the discs.
The electronics provided on the disc drive PWA primarily serve to control the operation of the HDA and to communicate with a host computer in which the disc drive is mounted. Generally, the top level functional blocks on the PWA include a read/write channel which controls the reading and writing of data from and to the discs, a spindle motor control circuit which controls the rotation of the spindle motor, and a servo control circuit which controls the position of the heads.
Each head typically includes a thin-film inductive write element to write data and a magneto-resistive (MR) read element to read previously written data. The write element generally comprises a ferromagnetic core about which a conductor is wrapped multiple times to form a coil. The core includes an air gap which is suspended in close proximity to the corresponding disc recording surface so that, as bidirectional write currents are pulsed through the conductor, magnetic fringing across the gap selectively magnetizes the surface.
Data are transduced from the surface by passing a read bias current through the MR read element and monitoring the voltage across the element; as the MR read element is subjected to the selective magnetization of the surface, the baseline electrical resistance of the element changes, allowing generation of a readback signal indicative of the data stored on the surface. Thus, each head is operably coupled to four conductor paths: two to accommodate the write currents supplied to the write element and two to accommodate the read bias currents applied to the MR read element.
A preamplifier/driver circuit is typically mounted to the side of the actuator assembly and includes a write driver circuit to apply the write currents to a selected write element during a write operation. The preamplifier/driver circuit further includes a bias current source which is sequentially connected to the appropriate read element to effect a read operation.
Because the data are stored as a series of magnetic flux reversals (xe2x80x9cflux transitionsxe2x80x9d) on the tracks, it is important to apply write currents that have well-defined transition characteristics. An ideal write current sequence generally resembles a square wave. However, factors such as electrical noise and transmission line effects can introduce significant distortion in a write current sequence, adversely affecting the ability of the read element to subsequently transduce the stored data. Such effects typically become more pronounced at higher data writing frequencies.
Prior art approaches to improving write current quality have included efforts to incorporate compensation circuitry (sometimes referred to as xe2x80x9cdamping networksxe2x80x9d) in the preamplifier/driver circuit. For example, U.S. Pat. No. 5,434,717 issued to Yoshinaga et al. discloses the use of damping resistors to reduce overshoot at current transitions. U.S. Pat. No. 5,357,379 issued to Gower employs a switchable resistor network to obtain optimal levels of impedance in both read and write modes. U.S. Pat. No. 5,880,626 issued to Dean discloses an active damping network formed from resistors, capacitors and transistors to compensate for oscillation (ringing) as the write current settles to the desired direct current (dc) value and to provide faster transition times as compared to straight damping resistor configurations.
While operable, as write frequencies continue to increase, there remains a continued need for improvements in the art whereby write current quality can be maintained at adequate levels to ensure reliable readback of the data. It is to such ends that the present invention is directed.
The present invention is directed to an apparatus for improving write performance in a disc drive.
In accordance with preferred embodiments, a disc drive is provided with a rotatable disc comprising a recording surface and an actuator assembly adjacent the disc comprising a flexible suspension assembly and a preamplifier/driver circuit which outputs a series of write currents indicative of data to be written to the recording surface.
The disc drive further has a head assembly, supported by the flexible suspension assembly adjacent the recording surface, which includes a write element and a write current shaping circuit. The write current shaping circuit modifies the sequence of write currents output by the preamplifier/driver circuit to improve operation of the write element in writing the data to the recording surface in relation to the modified sequence of write currents.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.